1. Field of the Invention
This invention relates in general to safety devices, and in particular to driver alertness monitors that alert the driver to the onset of fatigue and drowsiness.
2. Description of the Related Art
There are many devices in existence to alert drivers when they begin to fall asleep while operating a vehicle. Some have devices that attach to the driver's head for detecting when the driver's head begins to nod. These devices can have the unintended effect of causing neck and back fatigue, because drivers tend to hold their heads rigidly to prevent accidently triggering the alarm. Also, many drivers are unwilling to inconvenience themselves with putting on and wearing the devices. Other devices monitor minute movement of the steering wheel to determine whether the driver is alert and reacting to the environment. These devices are comparatively slow to detect a hazardous condition and often give false alarms.
Another class of device requires the driver to grip a device, either fastened around the steering wheel or held in the hand. U.S. Pat. No. 4,540,979, issued to Gerger et al., on Sep. 10, 1985, discloses a structure employing an air tube fastened around the circumference of the steering wheel. The tube is capped at one end and hermetically sealed to a pressure switch at the other end. The switch operates an alarm mechanism. The wheel must be gripped with sufficient force to actuate the pressure switch and silence the alarm. This device, and others like it, can also cause driver fatigue, as many drivers will grip the switch with excessive force in order to prevent the alarm from sounding.
A need remained for a driver alarm that is unobtrusive and convenient to use. A need also remained for a driver alarm that can respond rapidly, while still being sensitive to slow changes in driving conditions. A driver alarm that adapts itself to different drivers' gripping pressures was also desired. As always, a driver alarm that is reliable and less expensive was also desired.